[Bug fortran/57871] gfortran -freal-4-real-16 gives wrong result for selected_real_kind(1)

["sgk at troutmask dot apl.washington.edu" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57871

--- Comment #3 from Steve Kargl <sgk at troutmask dot apl.washington.edu> ---
On Wed, Jul 10, 2013 at 05:42:03PM +0000, kargl at gcc dot gnu.org wrote:
>   implicit none
>   integer,parameter:: p1 = selected_real_kind(1)
> 
> This initialization expression is requesting the type with
> smallest precision that exceeds 1.  With -freal-4-real-16,
> that type is double precision (ie kind=8).  The problem
> lies in gfc_simplify_selected_real_kind.  It has no knowledge
> of the -freal-*-real-* options.  The loop (lines 5447-5457)

(remove loop code)

> searchs the ordered set [24, 53, 53, 113] (on FreeBSD-i386) or
> [24, 53, 64, 113] (on FreeBSD-amd64).  In either case, the
> initialization expression returns REAL(4).  However, with
> -freal-4-real-16,  one might expect the ordered set to be
> searched is [113, 53, 64, 113] as REAL(4) has been promoted
> to REAL(16).

The results of running John's code are odder than what one
might expect.

The normal results:

% gfc4x -o foo foo.f90 && ./foo
 kind(1.0_p1)           4 precision(1.0_p1)           6
 kind(1.0_dp)           8 precision(1.0_dp)          15

One might expect the first line to be 8 and 15, respectively.

% gfc4x -o foo foo.f90 -freal-4-real-16 && ./foo
 kind(1.0_p1)          16 precision(1.0_p1)          33
 kind(1.0_dp)           8 precision(1.0_dp)          15

Here the default real kind is promoted to REAL(8), but literal
constants declared with a kind type suffix are not promoted.
The first line is the correct output, although one might
anticipate 8 and 15.  But, what may be surprising is that the 
double precision kind has been bumped to quad precision. 

troutmask:sgk[207] gfc4x -o foo foo.f90 -fdefault-real-8 && ./foo
 kind(1.0_p1)           4 precision(1.0_p1)           6
 kind(1.0_dp)          16 precision(1.0_dp)          33

I've always hated these type options as a lzy programmer's
crutch who refuses to properly port an algorithm from 
one precision to another.